The binocular parallax stereoscopic vision, which creates a three-dimensional effect according to the disparity between parallax images of a left-eye image and a right-eye image, is a technique in which an observer observes the left-eye image with the left eye and the right-eye image with the right eye at the same time, senses a disparity by mixing the two images in the brain, and perceives the depth from the degree of the disparity. The left-eye and right-eye images for the binocular parallax stereoscopic vision are produced by taking pictures with cameras placed at the left eyepoint and right eyepoint, respectively. Usually, the left and right images for the binocular stereoscopic vision are produced by taking pictures with a stereo camera or two cameras placed apart in a horizontal direction, in which case the depth of field at the photography is burned into the images. When proper focus is achieved for all the positions, the depth of field is burned as infinity. The images can also be taken twice with a single camera with moving the eyepoint.
Recently, the images can be produced by three-dimensional computer graphics (3D CG). Since the 3D CG simulates a real photographic system, when the left and right images are produced by the 3D CG, the term “photography” will be used below.
As for the left and right images thus produced, the quality of the images is decided by the performance the photographic means (camera or 3D CG-generating apparatus) originally has and its set conditions. The quality of the images refers to optical characteristics of the camera and lenses such as setting of the depth of field, focus position, focal length, composition and zoom (angle of view); chemical characteristics such as film and photosensitive emulsion; and characteristics of a photosensitive device such as a CCD, which are reflected on the images taken. As for the optical characteristics among them, the image is focused on a particular part of a subject in a normal photograph.
Generally, the setting conditions of the left and right images for the stereoscopic vision are set at approximately the same conditions except for the eyepoints at the photography, which are the same in the 3D CG. For example, when photographing with two cameras, pictures are taken using the same type of the cameras, lenses and films at the same exposure, at the same shutter speed, and at the same zooming. The left-eye image and right-eye image can be utilized as a single image for normal vision, and the individual images are completely the same image as the normal image (single image) taken form a single point of view.
(Binocular Rivalry)
In the binocular stereoscopic vision that observes the images having parallax with two eyes, there is a problem in that the focal adjustment is not effectively made because the observed images are flat. Apart from this problem, a simple stereoscopic vision, in which the left eye observes the left-eye image (normal photograph) taken from the left eye position, and the right eye observes the right-eye image (normal photograph) taken from the right eye position, will provide a very unnatural visual effect to a person who observes the external world binocularly in the real world. This is one of the reasons why the existing stereoscopic vision causes fatigue. Since the user is compelled to view the images based on the single lens with the two eyes, it is unavoidable that the unnatural feeling by the binocular stereoscopic vision is increased. In particular, using images such as photographic images that achieve focus in a wide range as the images for the stereoscopic vision, the unnatural feeling becomes conspicuous.
When this grows worse, many regions that are not mixed through the left and right eyes are perceived, so that binocular rivalry that perceives different visual images with the two eyes occurs, and the brain perceives disturbed, wavering images. Human beings primarily have a function to reduce the binocular rivalry when observing an object binocularly in the real world, which will be described in detail later.
(Application of Depth of Field of Stereoscopic Image)
One of the functions of reducing the binocular rivalry is a function based on the depth of field provided for the human eyes which observe an object in the real world in which the focal adjustment works effectively. Even in the case of the stereoscopic vision that observes images for the binocular stereoscopic vision, it is also possible to utilize the function by controlling the out-of-focus quantity that appears in the contents of the images for the stereoscopic vision. When observing the images for the binocular stereoscopic vision, the position of the focal adjustment of an observer is on the images for the binocular stereoscopic vision, in which case the focal adjustment of the eyes does not function effectively.
To display the left and right images for the stereoscopic vision without having the depth of field on a display (HMD in the technique), a technique is proposed which detects the position the observer of the displayed images gazes at, provides the depth of field to the displayed images according to the detected position, adjusts the focus on the gazing point when the gazing point moves, and provides the depth of field to the images using the new gazing point as a reference point (for example, see patent document 1).
Thus, as for the left and right images for the stereoscopic vision without the depth of field (in which the focus is achieved allover), the images with the depth of field are displayed by changing the reference point of applying the depth of field according to the movement of the gazing point of the observer.
The foregoing technique of applying the depth of field to the images has the following problems. It takes a long time for detecting the gazing position of the observer and for correcting the display image, and has a difficulty in achieving a natural view. In addition, an error of detecting the gazing position will result in excess eye fatigue. Furthermore, it is difficult to prepare the left and right images for the stereoscopic vision without the depth of field (in which the focus is achieved allover) and a depth map (an image that represents the distance from the eyepoint to the subject by gray levels). Thus, they cannot be obtained by ordinary cameras, and hence the apparatus becomes complicated, expensive and only a single person can view.
Moreover, to mix the left and right images for the stereoscopic vision having large parallax, they have too large a disparity, become images with a lot of binocular rivalry, and increase the physiological load of the stereoscopic vision observer. This will result in eye fatigue and pain, nausea and headaches.
The present invention is implemented to solve the fore going problems. Therefore it is an object of the present invention to mitigate the binocular rivalry caused by the stereoscopic vision, and to reduce the fatigue of the observer.
Patent document 1: Japanese patent application Laid-open No. 10-239634/1998.
Non-patent document 1: Hiroshi Inoue, “Explore the mysteries of stereoscopic vision” (The Optronics Co., Ltd., Published January 1999).
Non-patent document 2: Japan Society of Photogrammetry and Remote Sensing, “Method of viewing, taking and creating stereoscopic photograph” (Gihodo Shuppan Co., Ltd.).
Non-patent document 3: “Information processing of images and space”, Iwanami Lectures, Multimedia Information Science.